plucky (3) flopen.3bsd.gz

NAME

     flopen, flopenat — Reliably open and lock a file

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <sys/fcntl.h>
     #include <libutil.h>
     (See libbsd(7) for include usage.)

     int
     flopen(const char *path, int flags);

     int
     flopen(const char *path, int flags, mode_t mode);

     int
     flopenat(int fd, const char *path, int flags);

     int
     flopenat(int fd, const char *path, int flags, mode_t mode);

DESCRIPTION

     The flopen() function opens or creates a file and acquires an exclusive lock on it.  It is essentially
     equivalent with calling open() with the same parameters followed by flock() with an operation argument of
     LOCK_EX, except that flopen() will attempt to detect and handle races that may occur between opening /
     creating the file and locking it.  Thus, it is well suited for opening lock files, PID files, spool files,
     mailboxes and other kinds of files which are used for synchronization between processes.

     If flags includes O_NONBLOCK and the file is already locked, flopen() will fail and set errno to
     EWOULDBLOCK.

     As with open(), the additional mode argument is required if flags includes O_CREAT.

     The flopenat() function is equivalent to the flopen() function except in the case where the path specifies
     a relative path.  In this case the file to be opened is determined relative to the directory associated
     with the file descriptor fd instead of the current working directory.  If flopenat() is passed the special
     value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to
     a call to flopen().

RETURN VALUES

     If successful, flopen() returns a valid file descriptor.  Otherwise, it returns -1, and sets errno as
     described in flock(2) and open(2).

SEE ALSO

     errno(2), flock(2), open(2)

AUTHORS

     The flopen function and this manual page were written by Dag-Erling Smørgrav <des@FreeBSD.org>.